This invention relates generally to a method and apparatus for treating patients with adult-onset dementia. In particular, the invention relates to a method and apparatus for increasing the clearance of substances from the cerebrospinal fluid in certain patients with adult-onset dementia of the Alzheimer""s type.
The brain and spinal cord are encased within the cranium and vertebral column inside a thin membrane known as the arachnoid. The volume of the intracranial space is on average about 1700 ml. The volume of the brain is approximately 1400 ml, the volume of the intracranial blood is approximately 150 ml; the remaining 150 ml is filled with cerebrospinal fluid. The cerebrospinal fluid circulates within the subarachnoid space. It is formed principally by the choroid plexuses, which secrete about 80% of the total volume. The sources of the remainder are the vasculature of the subependymal regions, and the pia mater. The total volume of the cerebrospinal fluid is renewed several times per day, so that about 500 ml are produced every 24 hours.
The cerebrospinal fluid is absorbed through the arachnoid villi, located principally over the superior surfaces of the cerebral hemispheres. Some villi also exist at the base of the brain and along the roots of the spinal nerves. The absorptive processes include bulk transport of large molecules and as well as diffusion across porous membranes of small molecules. (Adams et al. (1989) xe2x80x9cprinciples of Neurology,xe2x80x9d pp. 501-502).
The principle on which this invention is based is that in some persons with adult-onset dementia of the Alzheimer""s type there is dysfunction of the cerebrospinal fluid resorptive mechanism, leading to the retention in the cerebrospinal fluid of substances which result in the histologic lesions associated with adult-onset dementia of the Alzheimer""s type, or which are neurotoxic, or both.
There are several examples of low-molecular weight proteins or peptides that are known to be present in elevated concentrations in the cerebrospinal fluid of persons suffering from adult-onset dementia of the Alzheimer""s type. For example, elevated levels of beta A-4 amyloid have been found in the cerebrospinal fluid of patients with early-onset Alzheimer""s disease. (Nakamura et al., (1994) xe2x80x9cAmyloid beta protein levels in cerebrospinal fluid are elevated in early-onset Alzheimer""s disease,xe2x80x9d Ann. Neurology 36:903-911). Beta A-4 amyloid is known to self-aggregate into molecules of amyloid of the type that typify the core plaques found in the brain in persons suffering from adult-onset dementia of the Alzheimer""s type. In fact, beta A-4 amyloid deposition in the brain is the only microscopic lesion specific for Alzheimer""s disease. Furthermore, beta A-4 amyloid has been shown to be neurotoxic. (Bush et al., (1992) xe2x80x9cBeta A-4 amyloid protein and its precursor in Alzheimer""s disease,xe2x80x9d Pharmac. Tera. 56:97-117). Beta A-4 amyloid is also a component of microscopic cerebral lesions known as neurofibrillary tangles, characteristically found in adult-onset dementia of the Alzheimer""s type.
Beta-2 microglobulin is another example of a low-molecular-weight protein whose concentration in the cerebrospinal fluid increases with age and reaches high levels in patients with adult-onset dementia of the Alzheimer""s type. (Martinez et al., (1993) xe2x80x9cRelationship of interleukin-1 beta and beta2-microglobulin with neuropeptides in cerebrospinal fluid of patients with dementia of the Alzheimer type,xe2x80x9d J. Neuroimmunology 48:235-240). Beta-2 microglobulin is associated with amyloid deposits in some tissues of patients on long-term renal hemodialysis. (Ono et al., (1994) xe2x80x9cFormation of amyloid-like substance from beta-2-microglobulin in vitro. Role of serum amyloid P component: a preliminary study,xe2x80x9d Nephron 66:404-407).
Another substance that accumulates in the cerebrospinal fluid in patients with adult-onset dementia of the Alzheimer""s type is tau, a component of the neurofibrillary tangles found in involved brain tissue. Tau concentrations in cerebrospinal fluid are regularly increased in this syndrome with eight fold increases present in half of the patients. (Arai et al., (1995) xe2x80x9cTau in cerebrospinal fluid: a potential diagnostic marker,xe2x80x9d Ann. Neurology 38:649-652).
In addition, the prior art also describes devices used to remove cerebrospinal fluid from a patient. Matkovich U.S. Pat. No. 5,334,315 describes a method and device that can be used to remove a body fluid from a patient, to treat that fluid to remove an undesirable component, and to return the fluid to the patient. Matkovich""s partial list of the kinds of deleterious or undesirable substances that can be removed from a fluid includes proteins, polypeptides, interleukins, immunoglobulins, proteases and interferon. The fluids from which these substances can be removed using the Matkovich apparatus include cerebrospinal fluid, blood, urine and saliva. Matkovich never suggests, however, that his method and apparatus could be used to treat patients suffering from adult-onset dementia of the Alzheimer""s type.
Kirsch et al. U.S. Pat. No. 5,385,541 describes a cerebrospinal fluid shunt mechanism used to treat hydrocephalus by draining cerebrospinal fluid into the patient""s abdomen, chest or vascular system. The system may include a one-way valve to prevent backflow. Kirsch et al. does not describe the use of such a system to treat adult-onset dementia of the Alzheimer""s type, however.
Ruzicka et al. U.S. Pat. No. 4,950,232 discloses another cerebrospinal fluid shunt system. As with the Kirsch et al. patent, Ruzicka does not suggest the use of his shunt system to treat adult-onset dementia of the Alzheimer""s type.
Chen et al. (1994) xe2x80x9cEffectiveness of Shunting in patients with normal pressure hydrocephalus predicted by temporary, controlled-resistance, continuous lumbar drainage: a pilot study,xe2x80x9d J. Neurol. Neurosurg. Psychiatry 51:1430-1432, describes use of a xe2x80x9csiliconxe2x80x9d catheter for draining CSF from the subarachnoid region into an external collection bag.
Although the prior art has recognized the presence of elevated concentrations of certain substances in the cerebrospinal fluid of persons suffering from adult-onset dementia of the Alzheimer""s type, the prior art has not provided a method of correcting this imbalance. One objective of this invention, therefore, is to provide such a treatment. Thus, in a preferred embodiment, the invention is a method for treating a patient for adult-onset dementia of the Alzheimer""s type by removing a portion of the patient""s cerebrospinal fluid, preferably (although not necessarily) by transporting the fluid to another portion of the patient""s body.
In addition, although the prior art has provided shunt devices to remove excess cerebrospinal fluid from patients suffering from hydrocephalus, the prior art has not recognized the use of these devices to treat adult-onset dementia of the Alzheimer""s type by removing cerebrospinal fluid that is not excessive in volume. Another objective of this invention is to provide an apparatus designed to transport cerebrospinal fluid at a controlled rate. The invention therefore also provides an apparatus for removing cerebrospinal fluid including (1) a conduit with a first opening and a second opening, the first opening of the conduit being adapted to be disposed in fluid communication with a space within a patient""s subarachnoid space, the second opening being adapted to be disposed in fluid communication with another portion of the patient""s body; and (2) a flow rate control device attached to the conduit.
The present invention provides methods, systems, apparatus, and kits for removing cerebrospinal fluid from a patient in a controlled manner, particularly for the treatment of Alzheimer""s disease. The cerebrospinal fluid is preferably removed at a rate sufficient to reduce or eliminate, preferably eliminate the progression of Alzheimer""s disease in patients. Usually, the removal rate will be in the range from 5% to 50% of the patient replacement rate (typically in the range from 250 ml/day to 300 ml/day), more usually from 10% to 20% of the replacement rate. At present, the preferred removal rate is in the range from 0.5 ml/hour to 15 ml/hour, preferably from 1 ml/hour to 5 ml/hour, more preferably from 1 ml/hour to 3 ml/hour, based on the average removal rate over a 24-hour period. It will be appreciated, however, that the particular removal rate which is effective with any individual patient may vary from within the preferred ranges set forth above, and any removal rate which results in significant lowering of the concentration of the factors associated with Alzheimer""s disease may have a therapeutic effect.
The invention will be described in more detail below with reference to the drawings.